This project is designed to continue the active site characterization of acrosin by defining the topography (structure) of acrosin's activity site so that specific affinity labeling acrosin inhibitors can be synthesized which may be used to inhibit fertilization. Agents that specifically bind to acrosin will be modified to become affinity labeling inhibitors. These inhibitors will be tested as to their specificity for acrosin and the functional amino acid residues will be determined.